User:Maiapalka1/Ice algae

To survive in the harsh sea ice environment, organisms must be able to endure extreme variations in salinity, temperature, and solar radiation. Algae living in brine channels can secrete osmolytes, such as dimethylsulfoniopropionate (DMSP), which allows them to survive the high salinities in the channels after ice formation in the winter, as well as low salinities when the relatively fresh meltwater flushes the channels in the spring and summer. Some sea ice algae species secrete ice-binding proteins (IBP) as a gelatinous extracellular polymeric substance (EPS) to protect cell membranes from damage from ice crystal growth and freeze thaw cycles. EPS alters the microstructure of the ice and creates further habitat for future blooms. Ice algae survive in environments with little to no light for several months of the year, such as within ice brine pockets. Such algae have specialized adaptations to be able to maintain growth and reproduction during periods of darkness. Some sea ice diatoms have been found to utilize mixotrophy when light levels are low. For example, some Antarctic diatoms downregulate glycolysis in environments with low to no irradiance, while upregulating other mitochondrial metabolic pathways, including the Entner−Doudoroff pathway which provides the TCA cycle (an important component in cellular respiration) with pyruvate when pyruvate cannot be obtained via photosynthesis. Surface-dwelling algae produce special pigments to prevent damage from harsh ultraviolet radiation. Higher concentrations of xanthophyll pigments act as a sunscreen that protects ice algae from photodamage when they are exposed to damaging levels of ultraviolet radiation upon transition from ice to the water column during the spring. Algae under thick ice have been reported to show some of the most extreme low light adaptations ever observed. Extreme efficiency in light utilization allows sea ice algae to build up biomass rapidly when light conditions improve at the onset of spring.